29642 - Mechanical Drawing T (L-Z)

Learning outcomes

The course supplies (gives) the bases for the interpretation and execution of technical design with methodologies of conventional representation,  and also to let the correlation between shape, function and productive processes for the functional elements of the machines and systems.

The course have the purpose to supply the bases required for the interpretation and the execution of the technical design.  After a first part dedicated to the geometric design are examined  the principal directions for the correct representation of particulars and global design. Is given special account to the function performed of each particular in the whole and to the influence of the productive system for a correct selection (choice)  of the shape and a detailed indication of  additional information to be included (dimensions, dimensional and geometric errors to be tolerable, etc.).

Course contents

1 – Introduction

Supports and Conventional Instruments for the design

Papers and format's standardization (unification) , design's reproduction (UNI 936). Sheet's bending (UNI 938). Inscription's panel (frame) (UNI 8187). Representation's scales (UNI 3967). Pencils and leads. Rules (straightedges) and squares. Compasses, curves, templates. Parallel straightedge and drawing machine.

 

Standard Lines and Inscriptions

The standardization related to the line types and their employment (UNI 3968), alphanumerical and numerical characters (UNI 7559), practical advice.

2 – The Representation

 

Basic geometrical construction

 

Bisection of a line segment, of an arc, of an angle. Perpendicular to a line from a given point: external, belonging to the line (medium point or end of line). Parallel to a given line (at a given distance or through a given point). Operation with the angles. Trisection of a right angle and of a straight angle. Division of a line in equal parts. Tangents to a circumference from an external point or from a belonging point. Internal and external tangents to two circumference. Circumference through 3 points, fillet of line and circumference with arc of given radius. Regular polygon: triangle, square, pentagon, hexagon and octagon with a given side or with circle circumscribing. Construction of a polygon with an unspecified number of side given the length of a side or the circle circumscribing. Plane curve (ellipse, parabola, hyperbole, oval, ovolo, involute).

 

Orthogonal projection method

 

Representation with orthogonal projection on two orthogonal plane of points, lines, planes. Belonging condition of a point to a line, of a line to a plane, of a point to a plane. Conditions of co-planarity, incidence and parallelism for lines; condition of parallelism for planes. The third plane of projection: determination of the third projection of points, lines, planes. Orthogonal projection of plane figure and solid figure. Rule for the detection and representation of hidden and no hidden lines. Determination of the third sight of mechanical parts known the other two.

 

 

Sections

 

Aim of sections: ideal plane of section. Plane sections of prism and pyramids. Sections of revolute solids (cylinder, cone, sphere and torus). Determination of the contour lines of the sections: generating lines method, auxiliary plane section method. Solids obtained by section plane (frustum of cone, pyramid, oblique cylinder).

 

 

Real shape of plane surfaces

 

Generality. Method of spreading out flat. Spreading out flat of points, lines, segment, plane figure on plane orthogonal to principal plane of projection.

 

 

Co-penetration of solids.

 

Generality. Co-penetration of prism and pyramid. Special use of auxiliary section plane. Determination of the intersecting lines of co-penetrating revolute solids: generating lines method, auxiliary section plane method, auxiliary sphere method.

 

 

Development of surfaces

 

Generality. Developments according to the criterion of the cutting of lowest length of prism, pyramid, cylinder, right or not cone. Developments of solid obtained from planes of section ( frustum of pyramid, of cone, of oblique cylinder, etc). Developments of parts of link of pipes of different section. Rough developments of spheres. Developments of intersection between cylinder and cylinder, cylinder and cone  with concurrent axis or not, normal or not.

 

 

Oblique and orthogonal axonometric projection, perspective

 

Reduction factors. Unified oblique axonometric projection (cavalier; UNI4819). Orthogonal parallel perspective orthogonal axonometric. Unified isometric axonometric (UNI4819). Axonometric representation of plane surfaces, prism and pyramid; true and approximate representation of circles, curves and revolute solids. Practical criteria for the representation in axonometric projection of mechanical parts.

 

 

3 – Technical design: standard and dimensioning

 

Standard

 

Generality and historical notes on the national and international agencies of standard (UNIM, UNI, ISA, ISO, CEN, CECA). Projection methods (UNI 3969). Sight: methods of the first dihedral (E) and the third dihedral (A), method of the pointer, of the particular sight, of the partial sight, of the local sight, of the overturning (UNI 3970). Sections along a plane, along two or plus consecutive planes, along parallel planes, along cylindrical surfaces of fixed directrix , partial sections and sections of symmetric parts; overturning sections in place or in proximity, subsequent sections; parts  not sub-divisible (UNI3971). Hutchings for the representation of materials in the sections (UNI 3972). Particular agreements of representation (UNI 3977). Criteria for the representation of linked parts.

 

Dimensioning

 

General criteria, dimensioning and reference lines, layout and reading of dimensions (UNI 3973). Dimensioning system ( in series, in parallel, in overlapping dimension,  joint dimensioning, in coordinate, in polar coordinate: UNI 3974). Particular agreements of dimensioning ( solid of revolution, circles, spherical surfaces, square, smoothed and rounded contours, regularly or irregularly placed elements etc.: UNI 3975). Criteria for choice of the reference elements and general instructions (rules) for a correct dimensioning. Layout of dimension in axonometric projection. Dimensioning of normalized parts (UNI 4820)

 

 

Type of design

 

Design global, set  or  subset, project, assembly, installation, exploded (UNI 9121). Placing numbers (UNI 8411). Component list (UNI ISO 7573). Design of finished product (technical design: UNI 4820). Search of functional conditions, pipes of dimension and criteria for the functional dimensioning. Structural design ( of production or of control).

 

 

Influence of the productive system on design and dimensioning

 

Modelling (moulding) and smelting

Plastic works and sheet (plate) works (forging, rolling, pressing, extrusion, drawing, shearing, punching, tracing (transferring), spinning, bending). Works with shaving removal: turning, milling, grinding drilling, reaming (boring), broaching, slotting, filing, planning ( short description of machinery and tools, working and feeding motions, main types of practicable works). Grooves (UNI ISO 4755, UNI 5709, UNI 5710, UNI 4386-75). Notes on working units, selected machinery, transferring lines and working center. Manufacturing dimension. Transfer from functional to manufacturing dimension or control.

   

 

 

4 – Materials

 

Technologic test: traction, hardness, impact resistance.

Grading of steel, cast iron, copper alloy, aluminium alloy, magnesium alloy etc.. A brief outline to the main thermal  processing. Use in the part or whole design of  the dimensional, qualitative standard, the supplying stage. Criteria for the choice of the materials and example (Manfè, Pozza, Scarato, Vol III, tavola 5.1, pag. 255).

 

 

5 – Standard Numbers,  tolerance, roughness

 

Generality: arithmetical and geometrical series, definition of ratio. Renard series (UNI 2016 and 2017).  

Dimensional tolerances: introduction, definitions, tolerance system ISO (UNI ISO 286).

Indication (sign) in the design of the tolerances (UNI 3976) and of the common tolerances (UNI ISO 2768).

Selection criteria of the tolerances. Standard shaft  and  standard hole system. Fit problems and applications. Recommended fits (UNI 7218-73). Set of dimensions allowed and evaluation of the resulting dimension tolerance. Criteria for the determination  of some deviations and tolerances in functional dimension chains, known the border (boundary) values of the functional condition or criteria for the evaluation of the functional condition tolerance, known the boundary size of the dimensions forming the chain.

Micro- and macro-geometrical errors ( preliminary talk).

Roughness: definition, correlation between the machining  type and the roughness (UNI ISO 4287 part I, UNI ISO 468, UNI ISO 4288).  Indication of the surface condition (UNI 4600).

 Geometrical tolerances: generality (UNI ISO 7226/1), references (UNI ISO 5459), graphical marks (UNI ISO 7083), principles for their uses (UNI ISO 8015).

Principle  of the maximum material (UNI ISO 7226/2).

 

6 – Joints

 

Generality on the stiff and elastic types of joint ( by friction, by obstacle, by friction and obstacle, by fusion (melting) and gluing).

Threaded connections; definitions (UNI ISO 5408), main unified threads ( metric: UNI 4534,4535, 4536; for pipelines with proof seal on the thread and not: UNI ISO 7, UNI ISO 228;

Whitworth (UNI 2708 and 2709); standard for the representation and dimensioning of screw, nut, bolt, dead hole threaded (UNI 3979); connection example: passing screw, biting (grip) and locked, etc.   

Tolerances for threaded connections (UNI 5541); bolts and nuts and strength classes (UNI ISO 4759, UNI 3740). Incomplete thread and grooves for internal and external threads (UNI 5709, UNI 5710, UNI ISO 4755). Through holes for screw (UNI ISO 273). Self anti-slackening systems (devices).

Joints through (by) hot riveting (UNI 141).

Joints shaft-hub through (by)  conical elements: taper ratio and cone angles (UNI 157-75).

Dimensioning and tolerance indication on conical elements (UNI 7618); notes on tolerance of taper ratio systems (UNI 7826), application examples ( Morse taper, etc…).

Force direct joints. Joints by stop rings (keyed), cotters, pins,  compensator rings.

Joints by keys ( sunk or not,  straight and round, saddle, gib-headed, tangential).

Joints by feathers (reduced or not, right and round, Woodruff). Cylindrical and conical shaft end elevation (UNI ISO 775).

Joints by cylindrical  splined shape with parallel side on internal spigot (UNI 8953) and with involute side (UNI ISO 4156). Complete and simplified representation (UNI ISO 6413), tolerances (UNI 8953 and UNI ISO 4156).

Joints by elastic rings.

Joints by cold riveting (UNI 750-756, UNI 7619, UNI 9063).

Joints by welding (UNI 11001, UNI 1307, UNI 1310).

 

 

7 – articulated joints (knuckles) and  guide

 

Knuckles and guide : introduction and first definitions.

Articulated joints [ around a axis ( forking and embossing), around a point (spherical knuckles)].

Guide for the straight sliding motion (prismatic guide ) and methods foe the clearance registration (ram slide gibs).

Guide for the straight rolling motion ( flat needle runner, guide for cross-roller and ball saddle, ball box, Tychoway-Rotax needle runner, Roundway roll devices).

Guide for the rotative motion: plain bearings: criteria of choice for the materials. Influence on the design of the working and lubrication   conditions.

Lubrication methods of bearing rotative motion guides (discontinuous feed: ball oiler, Stauffer lubricator  and with hexagonal head; continuous feed: spring lubricators, drip-feed  and wick oiler ) . Loop lubrication systems ( splash , ring and force feed ( pressure) lubrication).

Rolling rotative motion guide: rolling bearings. Generality, nomenclature of the unified types and their denomination. Criteria of choice on the bearing type, on the joint (dimensional) tolerances with the seats.

Criteria for the geometrical tolerances and roughness evaluation. Assembly problems. Ball and roller bearing assembly, ball and conical roller raking bearing assembly, assembly of axial single and double acting bearings.

Criteria for the lubrication and the protection of the rolling bearing and their influence on the design.

 

 

8 – seal system

 

Static seals: direct seal ( ogival, knife edge and conical), by inserted elements ( flat, toroidal, shaped, clad gasket, etc..).

 Dynamic seals: direct seal ( material test machine) by inserted elements with circular contact ( O ring, H ring, BK ring, Angus mechanical seal ring, etc..), by elements inserted by contact flat-frontal (V ring, etc…), and without contact (  Z lattens etc…).

Lip Seals for alternative mechanism.

 

 

9 – Mechanical drives

 

Rigid joints (coupling box, coupling shell, Sellers, coupling plate, coupling flange).

Elastic joints (coupling pin rubber coated, Pomini's joint, coupling dowel, Periflex joint, Giubo joint, Flak or Citroen joint)

Movable joints:relative motion permitted: axial (expansion joint, tooth joint), angular (universal joint), radial (Ohldam joint), rotation joint ( safety joint), axial and angular (flexible joint).

Manual clutch (tooth, single-plate and multi-plate clutch, electromagnetic)

Self-acting cluch (centrifugal, sopravanzo)

Transmission with belts and pulley (definitions, standards, design criterion for flat and V belts, applied examples)

Transmission with chains and timing belts (definitions, standards, design criterion, applied examples)

Transmission with friction wheel.

Transmission with gears (definitions, conventional representation, standard and applied examples)

Trapezoidal metric thread (UNI ISO 2901 and 2904). Transmission with worm gears, cam, connecting rod and  crank (definitions, standards, representation, applied example)

Readings/Bibliography

• Disegno Meccanico, Manfè, Pozza, Scarato, Principato Editore, 3 volumi.
• Disegno Tecnico Industriale, Chirone, Tornincasa, Edizioni Il Capitello.
• Disegno, Progettazione e Organizzazione Industriale, Straneo, Consorti, Principato Editore.
• Slides from lessons available at:http://diem1.ing.unibo.it/personale/liverani/teaching.htm

Teaching methods

Course configuration:
- theoretical room classes;
- practical laboratory activities drawing 2D drafts.

Assessment methods

Written and oral tests.

Teaching tools

Links to further information

http://diem1.ing.unibo.it/personale/liverani/teach_resources.htm

Office hours

See the website of Alfredo Liverani